Cannulas for dispensing fluid medicinal products are known which are used in particular for vaginal and anal applications and are generally sold in packages together with tubes or bottles containing one of said products.
Known cannulas are constituted by a barrel that is suitable to contain the product and inside which a plunger, rigidly coupled to the end of a pusher rod, can slide.
The barrel has an open end, which can be coupled to the dispensing outlet of the tube in order to introduce in said barrel the amount of product to be applied, and through which the introduced product is dispensed.
The opposite end of the barrel is closed by a back wall, which is provided with a hole in which the pusher rod is inserted slidingly; said back wall acts as an element for stopping the plunger in order to prevent its extraction.
The product introduced in the cannula is dispensed by acting on the pusher rod in the direction in which the plunger slides toward the open end of the barrel.
Cannulas are also known which are constituted by a barrel, which has open opposite ends and inside which a plunger is inserted slidingly, and by a pusher rod, which is separate from the plunger and can be coupled detachably thereto.
Undercuts or shoulders for abutment are formed at the opposite ends of the barrel and are suitable to stop the sliding of the plunger, preventing it from being extracted under the action of the pusher rod.
These last cannulas can be sold in packages that contain a single pusher rod, a plurality of empty single-use barrels to be used for the various applications, and one or more tubes of product.
In this case, one of the two ends of the barrels can be coupled to the dispensing outlet of the tube in order to introduce the product in the barrels, while the opposite end acts as a passage for the pusher rod.
As an alternative, the cannulas can be sold in packages that contain a single pusher rod and a plurality of barrels that are already filled with the product to be applied and are provided, at their two opposite ends, with closure plugs that are removed upon use.
However, these known cannulas are not free from drawbacks, including the fact that they have a significant space occupation, which makes them difficult and awkward to handle for users.
Another drawback of known cannulas, particularly those constituted by a rod that is detachably associable with the plunger, is that they are not straightforward and ready to use for users, since they in fact require additional assembly operations.
Another drawback of known cannulas is that the sliding of the plunger under the thrust applied to the rod often causes an uncontrolled dispensing of amounts of product that are unwanted because they are excessive or insufficient for the actual requirements.